The problem is that we will not move on from WW3, and famine, water depletion, resource exhaustion etc. are all existential problems for individual countries that will cause conflicts between previously peaceful nations. At some point the nations in conflict will have alliances and nuclear weapons, and people will use them when the choice is between that or starving to death by the millions. I would be somewhat more optimistic about humanity's ability to weather worsening circumstances if we didn't develop the human extinction button in all of our grand technological wisdom.

WW2 hit the higher layers of abstraction. You could still grow food plants in those countries during and after the war, but the governance structures were bombed. Climate change is the opposite. If you can't grow food, you're fucked.